An anti-reflection film is disposed on the display surface of various image display devices such as liquid crystal display device (LCD), plasma display panel (PDP), electroluminescence display (ELD) and cathode ray display device (CRT) to inhibit contrast drop due to reflection of external light or image. Therefore, an anti-reflection film is required to have a high physical strength (scratch resistance, etc.), chemical resistance and weathering resistance (resistance to moist heat, light-resistance, etc.).
As the anti-reflection coat (layer having a laminated structure of high refraction film, middle refraction film, low refraction film, etc.) to be used in the anti-reflection film there has heretofore been normally used a multi-layer coat comprising a lamination of thin transparent films of metal oxide. It has been usually practiced to form these thin transparent films of metal oxide by a chemical vapor deposition (CVD) method or physical vapor deposition (PVD) method, particularly vacuum deposition method, which is one of physical vapor deposition methods.
However, the vacuum deposition method for the formation of thin transparent film of metal oxide gives a low productivity and thus is not suitable for mass production, and a coating method having a high productivity has been proposed.
In the case where the anti-reflection film is prepared by a coating method, it is preferred that the high refraction film be prepared by incorporating inorganic fine particles having a high refractive index dispersed more finely in a film. It is known that when inorganic fine particles having a high refractive index are incorporated finely dispersed in a film in a larger amount, a transparent high refraction film having a higher refractive index is formed (see, for example, JP-A-8-110401, JP-A-8-179123, JP-A-11-153702, JP-A-2001-166104, JP-A-2001-188104, JP-A-2002-116323, and JP-A-2002-156508).
It is also known that the incorporation of titanium dioxide fine particles having an extremely high refractive index in a high refraction film is very effective (see, for example, JP-A-11-153702, JP-A-2001-166104, JP-A-2001-188104, JP-A-2002-116323, and JP-A-2002-156508).
However, in the case where titanium dioxide is used in the anti-reflection film as mentioned above, it is disadvantageous in that when the titanium dioxide fine particles are used under the sunshine over an extended period of time, organic compounds contained in the anti-reflection film are decomposed because the titanium dioxide fine paticles have a photocatalytic action, remarkably deteriorating the physical strength and optical properties of the anti-reflection film. This phenomenon occurs remarkably particularly with a high refraction film having titanium dioxide particles incorporated finely dispersed therein.
Further, the surface active agent and dispersant which are normally used as means for dispersing the inorganic fine particles are effective to keep the inorganic fine particles finely dispersed and hence form a transparent high refraction layer at the step of forming a high refraction layer, but it is very difficult to provide the high refraction layer thus obtained with a high physical strength (scratch resistance, etc.), chemical resistance and weathering resistance (resistance to moist heat, light-resistance).
Accordingly, it has been desired to prepare an anti-reflection film excellent in physical strength (scratch resistance, etc.), chemical resistance and weathering resistance (resistance to moist heat, light-resistance) by a coating method, but these requires have never been satisfied sufficiently.
On the other hand, the recent trend is for more liquid crystal display devices (LCD) to be provided with a wider screen having an anti-reflection film provided thereon.
A polarizing plate is an indispensable optical material for liquid crystal display device (LCD) and normally has a polarizing film protected by two sheets of protective film.
By providing these protective films with anti-reflection performance, drastic reduction of cost and thickness of display device is made possible.
The protective film used for polarizing plate needs to be adhesive enough to be adhered to the polarizing film. As a means for improving the adhesiveness to the polarizing film, it has been normally practiced to saponify the protective film, thereby hydrophilizing the surface thereof.
By effecting the saponification after the formation of an anti-reflection layer on the protective film, cost can be further reduced. However, in the case where the anti-reflection film is saponified to give a protective film for polarizing plate, the saponifying solution further deteriorates the physical strength (scratch resistance, etc.), chemical resistance and weathering resistance (resistance to moist heat, light-resistance) of the high refraction layer.